Scientists at Washington University in St. Louis have begun to measure noble gases present in the solar wind delivered to Earth by the Genesis spacecraft, the first sample return mission since the lunar Apollo missions in the late 1960s and early 1970s.
Genesis launched August 8, 2001 from Cape Canaveral in Florida and orbited the sun for two years at a point of gravitational stability between the earth and the sun, called the Lagrange L1 point. During this period, the craft collected solar wind from different solar “regimes,” periods when the wind flow can range from quiet to violent. Particles from these winds were collected on separate arrays individually deployed during each regime.
At the end of the mission, when the craft neared landing on September 8, 2004, a helicopter was supposed to swoop in, catch the parachutes, and lower Genesis to Earth. The chutes never deployed. The craft collided with the Utah mud flats and shattered into more than 10,000 pieces.
“Crashing on Earth was better than crashing some other place in the solar system. It’s just a question of determining the best way to clean the samples and choose the best samples for investigation to optimize our chances of success,” said Charles Hohenberg, Ph.D., professor of physics. Indeed, Hohenberg and University colleague Alex Meshik, Ph.D., senior research scientist, already have purified noble gases from bits of the aluminum shield. The Washington University researchers are among the first isotope-measuring researchers to analyze Genesis isotopes.
Although the sapphire and diamond targets, designed to collect solar wind from the “concentrator,” a device for enriching the rare solar wind elements, survived mostly intact, collectors from the other arrays were fragmented, but into large enough pieces to allow completion of all mission goals, said Hohenberg.
The arrays won’t be distributed to researchers until all are catalogued, said Hohenberg. In the meantime, scientists make do by studying the shiny aluminum originally designed to protect the craft’s batteries from solar heat.
Ions in the solar wind, which bombarded the aluminum at nearly 200 miles per second every day for two years, remain embedded in the metal. Contamination from water and dirt should not be a problem because noble gases are not very abundant in Earth’s atmosphere, and perhaps not found in the Utah mud, said Hohenberg.
The sun is made mostly of hydrogen; the second most abundant element is the noble gas helium. Other elements, decreasing in abundance with mass, are also present and collected in the Genesis arrays; more rare elements are detectable only in the concentrator targets. Study of the elemental and isotopic makeup of the sun is important for our understanding of the solar system because it is this starting material from which the solar system, including the planets, began, said Hohenberg.
Meshik and Hohenberg will study the noble gases helium, neon, argon, krypton, and xenon. The researchers want to understand the isotopic and elemental abundances of all noble gases.
Because solar wind in the different regimes streams at different velocities, scientists can use the abundances and the ratios of the noble gases to trace their origins and understand solar processes.
Wind speed important
Slow winds are the most common and the quietest. Velocity kicks up during different solar activities, such as coronal holes and coronal mass ejection, producing winds of different speeds. “The different types of winds might have different elemental and isotopic balances,” said Meshik.
Preliminary data collected by the scientists are promising enough that Hohenberg and Meshik have sent an official request to NASA to obtain pieces of the sapphire collectors from the different arrays. Because the aluminum heat shield was exposed constantly for the mission duration, scientists would be unable to distinguish the different solar events, but can measure the average solar wind.
“The beauty of the different arrays is that each were exposed to different solar wind regimes, and a monitor on the craft measured the speed of particles and triggered deployment of the specific arrays”, said Hohenberg.
Until now, lunar soil has given scientists a general idea of the composition of solar winds because the soil is saturated with solar material. “The precision is, however, not as good, and the composition is modified by different processes on the moon’s surface,” said Hohenberg.
Data from Genesis should allow precision and purity. The solar collector material will remain archived at Johnson Space Center in Houston, Texas. Materials from each collector array had different thickness, so they can be identified and catalogued in the Houston archive, to be released as requested by individual scientists, said Hohenberg.
Data obtained from Genesis will provide a starting point for some of the big questions in astrophysics.
“Analysis of one or two samples won’t put to rest the big questions. It doesn’t work like that. Genesis brought back samples of the solar winds, but this initial analysis is just the beginning. Studies with the refinement of analytical technique and the evolution of theory from its interpretation will go on throughout the 21st Century,” said Meshik. “It’s the beginning of a long journey.”